1. Field of the Invention
This invention utilizes sets of an arc-jaw collet mechanism to move a derailleur cable core of a person-powered vehicle such as a bicycle. The collet takes power from an electric relay whose input includes a battery and electric instruction from pressure and frequency transducers which sense pedal pressure and pedal velocity. Bridge circuits and solenoids link sensing logic with chain shifting apparatus.
2. Description of Related Art
Riding a bicycle inflicts two physiological problems:
1. Heavy pedal forces at a slow-pedal rate delivers less than optimum work from the human body and, if sustained, can induce muscle damage. PA1 2. High-velocity pedal travel at light pedal force also delivers less than optimum work from the human body yet accelerates fatigue.
Many human-power vehicles provide the rider with a manual control over pedal to wheel ratio. A hand-operated derailleur system is common.
However, manual management of levers or grips for as many as eight rear wheel sprockets and three pedalled sprockets does not usually offer optimized transfer of work from the rider into the bicycle.
One prior art automatic shifter (U.S. Pat. No. 4,598,920) automatically adjusts the pedal-to-wheel turning ratio for a set of rear wheel sprockets by sensing radial force from the rear wheel turning velocity and adjusting the rear-wheel driving chain with a derailleur guide. As vehicle speed increases, the pedal-to-wheel turning rate is reduced in the ratio steps available from a rear wheel set of sprockets.
A shifter described in application Ser. No. 08/181,294, now U.S. Pat. No. 5,407,396 (Chain Shifter) senses mechanical forces within a segment of chain in comparison to a pre-set threshold chain-force, with mechanical apparatus to adjust rear and front derailleur cable actions for an increased pedal-to-wheel turning rate. The shifter also senses a pattern of low chain forces and actuates cams to reduce the pedal-to-wheel turning rate. A pulse converter accepts oscillating signals from force sensors and moves derailleur cables.
A problem in shifting a derailleur cable in two directions with a combination of manual and automatic means is to disconnect automatic means from the cable when motion is not being applied. Conventional collets advance a shaft in one direction and then hold the shaft firmly. Such collets are commonly used as tooling for an engine lathe.